Surfactant alterations and lung fibrosis in a murine model of amiodarone-induced pulmonary fibrosis

Introduction: Amiodarone (AD) belongs to the class III antiarrhythmic drugs, and prolongs phase 3 of the cardiac action potential. Because amiodarone has a low incidence of pro-arrhythmic effects, it is now widely used for acute and chronic treatment of (life-threatening) arrhythmias, but the use is limited by the pulmonary toxicity. Amiodarone may cause an acute pulmonary syndrome that appears just like typical pneumonia – sudden onset of cough and shortness of breath (6–8% of all treatments). This condition usually improves rapidly once amiodarone is stopped. However, amiodarone may also cause a gradual and initially unnoticeable fibrosis of the lungs (2–4% of all treatments). Previous case reports indicate that some patients develop pulmonary fibrosis after a week of treatment, while others develop it after few months of continuous dose. There are no known factors that increase the incidence of amiodarone-induced pulmonary fibrosis in a particular individual. Thus, understanding the etiology of amiodarone induced pulmonary fibrosis is of considerable clinical value. For this purpose we have developed a murine model of amiodarone-induced pulmonary fibrosis and have investigated underlying alterations of surfactant processing in alveolar epithelial type II cells.

Methods: Amiodarone (AD) was dissolved in a solution of 4% ethanol, 2% sodium isothionate in ddH2O and 8mg/kg bw AD or vehicle buffer (control) were administered intratracheally via microsprayer to anaesthesized C57/Bl6 mice. Bronchoalveolar lavage fluids (BALF) and lung tissues were collected from all the sacrificed mice at days 3, 7, 14, 21 and 28 and prepared for histopathlogical examination (H&E, trichrome staining) or biochemical (Western Blots) characterization.

Results: As compared to controls AD treated mice showed cellular infiltration, extracellular matrix and collagen deposition. Development of patchy fibrosis was already visible as early as on day 7. While pro SP-C (˜21kDa), pro SP-B (˜42kDa, ˜25kDa, ˜19kDa) and mature SP-B forms were accumulated in the tissue, BALF levels of mature SP-B were significantly reduced in AD treated mice as compared to controls. Interestingly, increased levels of pro SP-B processing intermediates were detected in BAL of AD treated mice. In addition, total lung tissue phospholipid concentrations also increased in these mice.

Conclusion: These surfactant alterations might be involved in the development of amiodarone induced pulmonary fibrosis.